Convert the ixgbe PTP frequency adjustment implementations from .adjfreq to
.adjfine. This allows using the scaled parts per million adjustment from
the PTP core and results in a more precise adjustment for small
corrections.

To avoid overflow, use mul_u64_u64_div_u64 to perform the calculation. On
X86 platforms, this will use instructions that perform the operations with
128bit intermediate values. For other architectures, the implementation
will limit the loss of precision as much as possible.

This change slightly improves the precision of frequency adjustments for
all ixgbe based devices, and gets us one driver closer to being able to
remove the older .adjfreq implementation from the kernel.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Gurucharan <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>